The present invention relates to electrical grounding circuitry for magnetic disk drives and more particularly to grounding schemes designed to protect against electrostatic discharge (ESD) and electrical overstress (EOS), and to reduce background noises in read/write transducers utilizing magnetoresistive read sensors.
Magnetic head disk drive systems have been widely accepted in the computer industry as a cost-effective form of data storage. In a magnetic disk drive system, a magnetic recording medium in the form of a disk rotates at high speed while a magnetic read/write transducer, referred to as a magnetic head, xe2x80x9cfliesxe2x80x9d slightly above the surface of the rotating disk. The magnetic disk is rotated by means of a spindle drive motor. The magnetic head is attached to or formed integrally with a xe2x80x9csliderxe2x80x9d which is suspended over the disk on a spring-loaded support arm known as the actuator arm. As the magnetic disk rotates at operating speed, the moving air generated by the rotating disk in conjunction with the physical design of the slider lifts the magnetic head, allowing it to glide or xe2x80x9cflyxe2x80x9d slightly above and over the disk surface on a cushion of air, referred to as an air bearing. The flying height of the magnetic head over the disk surface is typically only a few tens of nanometers or less and is primarily a function of disk rotation, the aerodynamic properties of the slider assembly and the force exerted by the spring-loaded actuator arm.
A major problem that is encountered during manufacture, handling and use of magnetic recording transducers, referred to as heads, is the buildup of electrostatic charges on the various elements of a head or other objects which come into contact with the heads, particular heads of the thin film type, and the accompanying spurious discharge of the static electricity thus generated. Static charges may be produced for example by the presence of certain materials, such as plastics, during manufacture and subsequent handling of the heads. These static charges arc across the edge of the insulating layer between the magnetic pole tips and adjacent conductive layers which are exposed and positioned adjacent to the transducing gap at the air bearing surface facing the recording medium thus causing erosion of the pole tips and degradation of the transducer in reading and writing of data.
As described above, when an MR sensor is exposed to ESD, or even a voltage or current input larger than that intended under normal operating conditions, referred to as electrical overstress or EOS, the MR sensor and other parts of the head may be damaged. This sensitivity to electrical damage is particularly severe for MR read sensors because of their relatively small physical size. For example, an MR sensor used for extremely high recording densities will have a cross-section of 100 Angstroms (.ANG.) by 1.0 micrometers (um) or smaller. Discharge of voltages of only a few volts through such a physically small sensor, behaving like a resistor, is sufficient to produce currents capable of severely damaging or completely destroying the MR sensor. The nature of the damage which may be experienced by an MR sensor varies significantly, including complete destruction of the sensor via melting and evaporation, contamination of the air bearing surface, generation of shorts via electrical breakdown, and milder forms of damage in which the head performance may be degraded.
Magnetoresistive sensors, also referred to as xe2x80x9cMR heads,xe2x80x9d are particularly useful as read elements in magnetic transducers, especially at high data recording densities. The MR sensor provides a higher output signal than an inductive read head. This higher output signal results in a higher signal-to-noise ratio for the recording channel and allows higher areal density of recorded data on a magnetic disk surface.
Another method to increase the signal-to-noise ratio and therefore the areal density of recorded data on a magnetic disk surface is to decrease the noise. Noise is introduced into the MR head readings by the MR head and slider picking up undesirable external voltage/EMF fluctuations during operation of the disk drive. The noise can be reduced if the MR head and slider is properly grounded.
Kudo et al. U.S. Pat. No. 5,657,186 discloses a method of electrically connecting a slider to a grounding pad via a conductive resin.
A need therefore exists for providing a layer assembly that can be grounded to a desired potential.
A principle objective of the present invention is to provide a method to ground the stainless steel layer of an Integrated Lead Suspension (ILS) to a controlled ground potential.
In view of the foregoing objects, the present invention provides several methods to bring the stainless steel layer into contact with the copper layer through a layer of dielectric material. The first of these methods consist of creating a via from the copper layer, through the dielectric layer and onto the stainless steel layer exposing the surface of the stainless steel layer through the via. Conductive adhesive is then used to fill the via, creating a ground path between the stainless steel layer and the copper layer. The same can be done from the stainless steel to the copper layer. Instead of opening the via from copper layer to stainless steel layer, the via is opened from the stainless steel layer to the surface of the copper layer through the dielectric layer.
Instead of using conductive adhesive glue, solder can be used to create a grounding path between the copper layer and the stainless steel layer.
An alternative method calls for the recess of the copper layer layer and the dielectric layer, exposing the stainless steel layer. Solder is applied to the edge of this recess that overhangs the stainless steel and makes contact between the copper layer and the stainless steel layer.
A rivet can also be used to make contact between the copper layer and the stainless steel layer. A through hole is created through all three layers and a rivet attached that clamps down on the copper layer and the stainless steel layer.
A copper finger can also be used to make contact between the copper layer and the stainless steel layer. This method entails etching a copper finger which is connected to the copper layer. This copper finger is then pressed into contact with the stainless steel layer and welded in place.
The copper finger can also be sandwiched between the mount plate and the arm at the swage or between the mount plate and load beam at the layer weld process.
An alternative embodiment would be to create a via through the stainless steel layer and the dielectric layer to the surface of the copper layer. A dimple is then created on the load beam and during the assembly process, the load beam is pressed on top of the stainless steel layer and the dimple on the load beam is placed in the via. The dimple will make contact with the copper layer creating a ground path from the copper layer to the stainless steel layer.
Another embodiment is to punch a through hole through all three layers. By punching a through hole, the stainless steel will smear through the dielectric layer and make contact with the copper layer. Alternatively, the through hole can be punched through the copper layer to the stainless steel layer and in this case, the copper will smear through the dielectric layer and make contact with the stainless steel layer.